湖北钉螺种群结构动态变化的现场观察

目的了解湖北钉螺种群结构1年周期内动态变化,为钉螺控制提供科学依据。方法选择河滩、沟渠有螺环境各1处,于每月中旬采用系统抽样法进行连续1年的钉螺调查,调查指标包括钉螺的死活、性别、螺旋数、钉螺体长与体宽、生殖腺发育状况(颜色深浅、生殖腺与肝脏长度的比值),以及土壤螺卵含量。同时,测量土壤温度和湿度,以及收集环境所在地的气温和日降雨量等气象数据。结果钉螺存活率、活螺密度与土壤温度、气温呈正相关。钉螺存活率略呈双峰型,峰值在5~6、9月份;活螺密度河滩环境呈双峰型,峰值在7、9月,而沟渠以4~5月最高。钉螺体长(L)与体宽度(W)回归方程,L_(河滩)=2.355+1.678W(F=2 989.43,P0.01),而L_(沟渠)=0.478+2.091W(F=2 989.43,P0.01)。河滩环境钉螺体长在4.07~11.81 mm之间,平均值为(8.98±0.92)mm;沟渠钉螺体长在3.63~9.92 mm之间,平均值为(7.03±0.82)mm。钉螺河滩和沟渠环境钉螺的螺旋数分别以5~8个和4~7个为主,其中河滩环境螺旋数≤5、沟渠环境螺旋数≤4的钉螺构成比分别以5、9月份最高,均为20%左右。河滩、沟渠钉螺雌雄比分别为1.66∶1和1.22∶1。雌雄钉螺的生殖腺发育基本呈同步变化,丰盈期为4~5月和9~10月。土壤螺卵含量月间差异均显著,河滩以6月份最高(100.8个/0.1 m~2),沟渠以5月份最高(82.5个/0.1 m~2)。结论 4-5月和9-10月是钉螺繁殖、世代交替的主要时节,应作为血吸虫病易感地带的钉螺药物灭杀时间节点。

Dynamic change of population structure of Oncomelania hupensis

Objective To understand the successive dynamic change of population structure of Oncomelania hupensis during a one?year period, so as to provide the evidence for snail control. Methods A river beach and a ditch infested with O. hupensis snails were selected and longitudinally investigated in the midmonth during one year. The snail survey indices included the survival status, gender, number of whorls, length and width of shell, and gonad development status （measured by the color depth of gonad and the length ratio of gonad to liver）, and the monthly snail eggs in the soil were collected and counted simultaneously. In addition, the temperature and humidity of the soil and the daily data of air temperature and precipitation were measured or collected during the study period （every month）. Results Both survival rate of snails and live snail density at the two environments were positively correlated with the temperatures of air and soil. With a slight bimodal distribution, the snail survival rate peaked from May to June, and in September. The living snail densities got the highest level in July and September in the river beach, and from April to May in the ditch. The regression equations of snail length （L） and width （W） were Lbeach = 2.355 + 1.678W （F = 2 989.43, P < 0.01） and Lditch = 0.478 + 2.091W （F = 2.989.43, P < 0.01）, respectively. The snails were the ones with 4.07-11.81 mm in the length （8.98 ± 0.92） mm in the river beach, and the snails were the ones with 3.63?9.92 mm in the length （7.03 ± 0.82） mm in the ditch. The main snails were the ones with five to eight whorls of shell in the river beach and four to seven whorls of shell in the ditch. The proportions of snails with less than or equal to five whorls （in the river beach） and four （in the ditch） were the highest in May and September, about 20%. The ratios of male and female snails were 1.66 in the river beach and 1.22 in the ditch, respectively. The gonad development status of male and female snails was basically synchronous and had a bimodal abundance period ? from April to May and September to October. The numbers of snail eggs in the soil among months were significantly different, reaching the highest in June in the river beach （100.8/0.1 m2）, and May in the ditch （82.5/0.1 m2）. Conclusion The principal periods of breeding and alternation of generations of snails are April?May and September?October every year, which should also be the optimal time for mollusciciding in schistosomiasis susceptible zones.